The Experts: Do Nord-Lock washers work with oversized holes?

Q: How can I apply Nord-Lock to slotted/oversized holes?

A: In some designs slotted or oversized holes are used in order to facilitate positioning of parts during assembly or adjustment/alignment of clamped parts.

However, a slotted hole results in a reduced contact surface between the fastener and substrate material. Therefore the compressive stress in the substrate material increases and the edges of an enlarged hole may deform.

By using washers with increased outer diameter the load can be distributed over a larger surface and the compressive stress in the substrate material can be reduced. In order to optimise the load distribution it is beneficial to use flanged fasteners. In this way, bending of the washers and deformation of the edges of the slotted holes and excessive settlements can be avoided even when the fasteners are tightened to a high preload.

Nord-Lock offers washers with an enlarged outer diameter, so called “sp”, in sizes up to NL36sp in steel and NL30spss in stainless steel for use on enlarged or slotted holes.